1. Field of the Invention
The present invention relates to a floppy disk drive (hereinafter referred to as xe2x80x9cFDDxe2x80x9d) into which a floppy disk is loaded and, more particularly, to a chucking device for chucking a floppy disk.
2. Description of the Related Art
Referring to FIG. 9, a floppy disk 1, which is a recording medium, has a disk cartridge in which a thin-film recording disk 1a is housed in a case 1b. A top surface of the case 1b has a read/write window 1d, a shutter 1c that can be opened or closed being installed to cover the read/write window 1d. 
A center hub 2 formed of a metal disc is inserted to a central portion of the recording disk 1a of the floppy disk 1. In the center hub 2, a central opening 3 having a nearly square shape is formed at its central portion, and a driving hole 4 having a nearly rectangular shape is formed in its peripheral portion. The driving hole 4 has a front edge 4a at its front as observed in a counterclockwise direction in the drawing and an outer edge 4b in a direction away from the central opening 3.
In general, the floppy disk 1 is inserted in an FDD or a magnetic disc unit, not shown, the recording disk 1a is rotated in the FDD, and the recording disk 1a is partly exposed through the opened shutter 1c and the write/read window 1d to input or output of data to be recorded. The recording disk 1a can be easily inserted in or removed from the FDD while it is housed in the case 1b. The recording disk 1a must be accurately aligned with a rotating axis of the FDD, and its rotational speed must be accurately controlled. For this reason, a conventional FDD has been using a chucking device as shown in FIG. 7 and FIG. 8.
The FDD is provided with a rotor yoke 101 formed of a metal disc, and rotationally driven in a predetermined direction (indicated by xe2x80x9cDxe2x80x9d in the drawings) by a motor, not shown. A magnetic disc or a chucking magnet 102 is fixed on the rotor yoke 101.
A shaft 103 is installed in a standing manner at a center of rotation O of the rotor yoke 101. The shaft 103 extends, passing through an aperture 102a at the central portion of the magnetic disc 102, and loosely inserted in the central opening 3 of the center hub 2. In this case, xe2x80x9cloosely insertedxe2x80x9d means that the shaft 103 freely moves horizontally and vertically within a predetermined range.
A driving pin inserting hole 104 having an arc shape is formed along a circumference in a peripheral edge portion of the rotor yoke 101. A driving arm 105 formed in an arc shape along the circumference is loosely installed in the driving pin inserting hole 104. The driving arm 105 has a driving pin 106 that extends upward and is formed on a distal end portion 105a oriented in a rotational direction D of the rotor yoke 101. The driving pin 106 loosely penetrate a front aperture 102b formed in the magnetic disc 102 and is loosely inserted in the driving hole 4 of the center hub 2. Furthermore, the distal end portion 105a has flanges 105c and 105c that loosely clamp a portion of the rotor yoke 101 near the front of the driving pin inserting hole 104 and support the front portion of the driving arm 105 such that it can be moved horizontally and vertically within a predetermined range.
A rear end portion 105b at a rear of the driving arm 105 extends in a hook shape toward a rear on a top surface of the rotor yoke 101 from a trailing end of the driving pin inserting hole 104 formed in the rotor yoke 101, and receives a swinging shaft 108, which protrudes from a top surface of the rotor yoke 101, in a receiving hole 105d in a rear opening 102c formed in the magnetic disc 102. Thus, the driving arm 105 can horizontally swing around the swinging shaft 108 within a range of a width of the driving pin inserting hole 104.
A ferromagnetic plate 109 is installed on a top of a main body of the driving arm 105. The entire driving arm 105 is magnetically attracted to the magnetic disc 102, constantly pushing the driving pin 106 upward.
When the floppy disk 1 is inserted in the FDD, the recording disk 1a is placed on the rotor yoke 101, the center hub 2 attached to the recording disk 1a is magnetically attracted to the magnetic disc 102, and the central opening 3 of the center hub 2 receives the shaft 103 adjacent to the rotor yoke 101. At this time, the driving pin 106 projecting upward from the magnetic disc 102 is inserted in the driving hole 4 of the center hub 2.
When the driving pin 106 is not in the driving hole 4, the driving pin 106 is pushed by the center hub 2, so that it is pushed in the driving pin inserting hole 104 against the attraction force by the ferromagnetic plate 109 to prevent the driving pin 106 from projecting to the center hub 2.
The motor (not shown) is started, and while the rotor yoke 101 is being turned once in a direction D, a top portion of the driving pin 106 is slidably rotated on a bottom surface of the center hub 2 and received in the driving hole 4, then raised in the driving hole 4 by the attraction force of the ferromagnetic plate 109. As the rotor yoke 101 further rotates in the direction D under this condition, the driving pin 106 comes in contact with the front edge 4a of the driving hole 4. At the same time, the driving arm 105 swings about the swinging shaft 108 in a direction such that the driving pin 106 moves away from the center of rotation O by a load of friction between a head and the recording disk (medium) 1a, causing the driving arm 105 to come in contact also with the outer edge 4b of the driving hole 4. As a result, the driving pin 106 is supported by being abutted against the two sides, namely, the front edge 4a and the outer edge 4b of the driving hole 4.
The shaft 103 is supported by being abutted against two sides 3a and 3b of the central hole 3 of the center hub 2 on sides opposing (or away from) the driving pin 106, the center of rotation O being between the two sides. Under this condition, the center of the recording disk la coincides with the center of rotation O of the rotor yoke 101, thus completing a chucking process. In this state, the recording disk 1a of the floppy disk 1 rotates according to a controlled rotational speed of the rotor yoke 101.
As set forth above, the conventional chucking device employs the driving arm to abut the driving pin 106 against the two sides, namely, the front edge 4a and the outer edge 4b of the driving hole 4.
The driving arm 105, however, has a supporting point provided by the driving shaft 108 and the receiving hole 105d of the rear end portion 105b; hence, a clearance therebetween tends to vary, presenting a problem in that an accuracy of the clearance must be controlled.
Furthermore, the driving shaft 108 providing the supporting point must be sufficiently high to prevent it from slipping out of the receiving hole 105d of the rear end portion 105b of the driving arm 105. If the height is not accurately set, then the position of the supporting point easily varies, leading to a possibility of a failure of writing or reading data to or from the recording disk 1a. 
There has been another problem in that the driving arm 105 is provided with a swinging shaft 108 that has a sufficient height for preventing it from slipping off the receiving hole 105d of the rear end portion 105b, requiring extra time and effort for machining and assembling the components with resultant increased manufacturing cost.
Accordingly, an object of the present invention is to provide an FDD chucking device which is capable of preventing eccentric rotation of a recording disk by using a reliable and inexpensive means to permit consistently accurate writing and reading, permits easy assembly, and controls manufacturing cost.
To this end, according to one aspect of the present invention, there is provided an FDD including: a magnetic disc on which a center hub of a floppy disk is rested and which rotates in a predetermined direction; and a driving arm equipped with a driving pin on one end thereof, wherein the driving pin is inserted in a through hole provided in the magnetic disc, the driving arm is loosely fitted to the magnetic disc, and a part of a peripheral portion of the through hole presses the driving pin by rotation of the magnetic disc so as to rotate the center hub of the floppy disk by the driving pin.
In a preferred form of the present invention, an engaging member is provided on the other end of the driving arm, and the engaging member and the driving pin are loosely fitted to a locking portion provided on the magnetic disc.
In another preferred form of the present invention, a part of a peripheral portion of the through hole is formed to be a slant portion inclined at an acute angle with respect to a rotational direction of the magnetic disc.
According to another aspect of the present invention, there is provided an FDD chucking device including: a magnetic disc on which a center hub of a floppy disk is rested and which rotates in a predetermined direction; and a driving arm equipped with a driving pin on one end thereof and an engaging member on the other end thereof, wherein the magnetic disc has first and second through holes and first and second locking portions composed of thin-wall portions exposed in the through holes, and the driving pin is inserted in the first through hole, while the engaging member is inserted in the second through hole, and the driving pin and the engaging member are locked by the first and second locking portions to thereby loosely fit the driving arm in the magnetic disc.
In a preferred form, the second locking portion has a protuberance on its top surface, and the engaging member is locked between the protuberance and an inner wall of the second through hole.
In another preferred form, the driving arm is provided with a ferromagnetic plate, and the ferromagnetic plate is attracted and retained to the magnetic disc to thereby project the driving pin from the through hole.